Amount of light falling on a surface is measured in?

The amount of light falling on a surface is measured in footcandles. A footcandle is defined as the illuminance on a surface that is one foot away from a uniform light source of one candela. This measurement reflects the intensity of light reaching a specific area and is crucial in various applications, particularly in design and safety for ensuring adequate visibility in a given space.

In contrast, lumens measure the total quantity of visible light emitted by a source, not the light that actually reaches a surface. Candlepower refers to the luminous intensity of a light source in a particular direction, indicating how much energy light is produced but not the distribution on surfaces. The Color Rendering Index (CRI) is a metric that evaluates how accurately a light source shows the colors of various objects compared to a natural light source, and does not pertain to the quantity of light falling on a surface. Thus, footcandles are the appropriate unit for measuring illuminance on a surface.